Devices requiring two or more tuners or frequency converters are well known. Plug-and-Play™, TiVo™, set-top boxes and televisions with picture-in-picture are examples of such devices. In the current state of the art, tuners are often separately packaged and engage separate portions of the device in order to minimize tuner interference. By maintaining some physical separation between tuners of such devices cross-talk and interference generated by the tuners can be minimized. However, the ability to maintain useful separation between tuners has been limited as the size of such devices continues to diminish. Development is also being made to integrate two or more tuners on a single circuit board. One challenge of miniaturization of such devices is the elimination or minimization of multi-tuner interference. RF shielding and/or extensive RF filtering and circuitry is often needed to suppress tuner generated interference.
To improve sensitivity and selectivity in modem tuners, there is a need to minimize noise and spurious frequency elements (spurs) that can occur in the tuner output. Spurs can be generated from multiple sources, such as internal switching, quantization noise, or other device components. As described in more detail below, tuners can also be sources of spurs. The identification of intra-tuner spurs in multi-conversion tuners is the subject of U.S. Ser. No. 10/319,118, entitled “System and Method for Discovering Frequency Related Spurs in a Multi-Conversion Tuner,” hereby incorporated by reference herein. In a multiple tuner device, spurs may include intra-tuner spurs and inter-tuner spurs generated by local oscillators of the tuners. Other spur types and sources also exist.
Single conversion and multiple conversion tuners are well known. Such tuners often utilize one or more local oscillators in the mixing process. Examples of double conversion tuners are shown as tuners 106 and 108 in FIG. 1. In a double conversion tuner, an incoming signal at frequency ffIN is mixed with a signal at frequency ffLO1 from a local oscillator (LO) to produce a signal at an intermediate frequency fIF. This signal is then mixed with a signal at frequency fLO2 from a second local oscillator to produce the desired output frequency fOUT. The frequencies of the first and second LO signals are usually selected so that the first IF signal and output signal occur either at a specific frequency or within a specified frequency range.
Devices having multiple tuners are also well known. A dual tuner system is shown as tuner system 100 in FIG. 1. Specifically, tuner system 100 includes a pair of double conversion tuners 106 and 108, although a multiple tuner system may comprise other tuner configurations (e.g., single conversion tuners or a combination of single and multiple conversion tuners). In a dual tuner system, multiple LO's may be utilized to produce two desired output frequencies, fOUT,1 and fOUT,2. In the example of FIG. 1, each tuner 106 and 108 includes a pair of mixers, shown here as mixers 110 and 112 and mixers 114 and 116, respectively, wherein the fLOi,j signals are mixed to produce fOUT,1 and fOUT,2.
To improve sensitivity and selectivity in modern tuners, there is a need to minimize noise and spurious frequency elements (spurs) that can occur in the tuner output(s). Spurs can be generated from multiple sources, such as internal switching, quantization noise, or other device components. As described in more detail below, tuners can also be sources of spurs. Generally any or all spurious signals are undesirable and, if possible, should be reduced or eliminated to enhance tuner operation.
Single tuner systems can have intra-tuner spurs related to the frequency harmonics of one or more associated local oscillators. In single-conversion tuners, spurs may be related to the harmonics of its associated local oscillator. In double conversion tuners, spurs may be related to combinations of the harmonics of the first and second local oscillators frequencies (fLO1 and fLO2). The identification of intra-tuner spurs in multi-conversion tuners is the subject of the above referenced patent application entitled “System and Method for Discovering Frequency Related Spurs in a Multi-Conversion Tuner.”
Multiple tuner systems can be affected by both intra-tuner spurs and inter-tuner spurs. As in a single tuner system, each tuner of a multiple tuner system may be affected by intra-tuner spurs related to the harmonics of its own local oscillator(s). Additionally, each tuner in a multiple tuner system may be affected by inter-tuner spurs which are spurs related to frequency harmonics of local oscillators of both the subject tuner and any neighboring tuner(s).
An efficient method of eliminating or minimizing the effects of spurs in multiple tuner systems would be desirable.